Beneficiation of low grade coal



s. E. ERICKSON BENEFICIATION OF LOW GRADE COAL sept. 28, 1943.

Filed Jan. 29, 1941 2 Sheets-Sheet 1 vINVENTOR ri/fnv f. w @fsa/v.

A TTORNE Y.

Sept. 28, 1943. s. E. ERICKSON 2,330,479

BENEFICIATION OF LOW GRADE COAL Filed Jan. 29, 1941 2 Sheets-Sheet 2 FIG. 2.

f PrP/'75 1N VENTOR.

BY w gub ATTORNEY.

Patented sept. z's, 1943 oFF-ICE y A,

BENEFICIATION OF LOW GRADE COAL Stephen E. Erickson,

Springdale, Conn., assignor to Chemical Construction Corporation, New

York, N. Y., a corporation o1' Delaware Application January 29, 1941, Serial No. 376,447l

' In Brazil April 5, 1940 1 Claim.

'I'his invention relates to the beneiciation of low grade coal. More particularly the invention (cl. ais-94) c relates to the recovery of both coal and pyrite values from a low grade coal composed of good coal, bone coal, slate, and pyrite. In particular this invention relates to the treatment of low grade coal in Which the good coal occurs in ne grains and therefore requires crushing Vto a comparatively ne degree in order to liberate 'the good coal from the accessory material.

A coal of this type occurs in Brazil. For some time attempts have been made to produce a low ash coal suitable for locomotive fuel from this low grade material but ordinary coal Washing methods on this type coal do not give asatisfactory low ash coal and also do not permit the recovery of the pyrite as a secondary product which is suitable for use in acid manufacture. When the procedure of the present invention is applied to crude coal of this type, a relatively high grade coal, suitable for combustion purposes, and a pyrite by-product which can be used for acid manufacture are readily produced. The term "pyrite as used in this application refers to any or all sulfide bearing materials occurring in low grade coal.

The flotation of coal using standard iiotation reagents which are for the most part hydrocarbons such as kerosene accompanied if necessary by suitable frothers has been used on a rather large scale in the past for reducing the ash content of the coal. cedures have been used to recover the coal values from waste slush or culm, such procedures being described in the Crawford and Grine U. S. Patent 2,136,074 in which the culmis separated into two or more size fractions and each size oated separately using different flotation procedures for each of the sizes. The Headley U. S. Patent 2,136,341 describes a process for recovering coal values from a slush culm by notation which comprises iiotation of the coal nes followed by screening or classification of the iiotation tailing, rejecting the fine sizes and then subjecting the coarse portion to flotation to recover a low ash coal concentrate. c

Various gravity separation methods have also been employed in the past for recovering coal values from coal contaminated with high ash material. Among such specific gravity concentration methods are those such as tabling, Jigging, and iioat and sink methods. v-

The primary purposes of the above coal treating processes were for the purpose of obtaining a clean coal concentrate having a low ash value More recently notation pro` and were not concerned with the recovery of materials other than coal that might be present, as for example the pyrites. While many of these past procedures are commercially successful in obtaining a high grade coal concentrate from certain types of coal, they are not at all successful in recovering the coal and pyrite values from a low grade coal containing good coal, which is present in relatively fine-size particles, bone coal,

yslate and a relatively high percentage of pyrite.

The beneciation of such low grade coal has been a serious problemin the coal industry heretofore as there has been no economical method for recovering the values therefrom. While the problem is of little economical importance in the United States it is of very great importance in countries that do not have an abundance of high grade coal such as, for example, Brazil, but do have large amounts of low grade pyritecontaining coal.

In accordance with the present invention a coalv treating process is provided which is particularly useful for the beneflciation of low grade coals containing pyrite. The flow scheme employed in the present invention results in the recovery of a clean coal product having a relatively low ash content and also the recovery of a pyrite product suitable for acid manufacture.

In carrying out the present invention 'a low grade coal containing good coal, bone coal, slate, and pyrite is subjected to a crushing operation and the crushed coal issubjected to froth ilotation producing a concentrate and tails. The flotation concentrate is then subjected to a gravity concentration method resulting in the production of a relatively clean coal concentrate. The ilotation tailings are also subjected to a gravity concentration method and result in the production of a pyrite concentrate, suitable for use in acid manufacture.

The present invention is not concerned with any particular type of flotation reagent and it is an advantage of the invention that it is applicable to the standard reagent combinations. Similarly the invention may be used with various types of flotation equipment.

The invention is also not broadly concerned With the particular type of crushing. equipment that is'employed to -crush the coal, nor in any particular type of screen or classifier that may be used to eiect sizing of the crushed coal prior to flotation. The invention likewise is not particularly concerned with a particular type of gravity concentration apparatus which is employed to treat the flotation concentrates and tails.

The invention will be described in greater detail in conjunction with typical flow schemes which have been found to result in good recovery of clean coal and pyrite products from low grade coals.

Figure 1 is a diagrammatic flow sheet of a process in which the crushed coal is divided into a coarse fraction and a fine fraction, each fraction being then subjected to a flotation treatment followed by gravity concentration of flotation products. t

Figure 2 is a diagrammatic flow sheet of a process in which the crushed coal is subjected to a screening operation prior to flotation, the oversize being returned to the crushing circuit and the undersize being subjected to flotation followed by gravity concentration of the flotation products.

The operation of the present invention will be readily apparent by referring specifically to the flow scheme of Figure 1 in which a run of mine low grade coal containing pyrite from a Brazilian coal deposit in which the good coal particles were --35 mesh in size and in which the pyrite was satisfactorily liberated from attachments by crushing to mesh is fed into a suitable crushing circuit which may consist of a coarse jaw crusher followed by a roll crusher or mod-mill, if desirable, which results in the production of a -35 mesh material. The crushed material is then fed onto a screen which permits the -35 mesh material to pass through and the oversize or plus 35 mesh is returned to the crushing circuit. 'Ihe undersize or -35 mesh material is then subjected to a suitable classifying operation which results in the production of a coarse fraction approximately plus 65 mesh and a ne fraction which is approximately -65 mesh. This classifying process may be accomplished by any suitable classifier preferably, however, a screen is used because of the more desirable size control obtained. 'I'he coarse fraction, plus 65 mesh, is now subjected to a froth flotation treatment in the presence of any suitable collector and frothing reagent such as, for example, fuel oil and an alcohol frother. The flotation concentrate contains a high percentage of coal which, however, has also a. high '.ercentage of ash.- The clean coal is then recovered from this concentrate by subjecting to a gravity concentration treatment. The gravity concentration is preferably' carried out by tablng.

subjected to tabling concentrations to result in the production of a fine fraction clean coal concentrate and a fine fraction pyrite product respectively. The data in the following table will illustrate in greater detail the operation of the present invention in accordance with the flow scheme of Figure 1.4

EXAMPLE l A Brazilian crude coal was crushed and classied into -35 plus 65 mesh, and -65 mesh sizes.v Each size was then separately subjected to flotation and the flotation products separately subjected to a tabling treatment.

Minus 35 plus 65 mesh size (coarse fraction) Condition pulp with 0.50 lb./ton fuel oil prior t0 float.

Float at 20% solids.

frother-0.15 to rougher, 0. 10 to cleaner.

Rougher time-3 minutes.

minutes.

Cleaned conc. tabled for removal pyrite.

Cleaner time-2 Results Product Weight Ash Per cent Per cent Feed 34. 44 Rougher tail 44. 88 50. 04 Cleaner tail flot. 6. 53 3B. 26 Cleaner conc. flot 48. 57 19. 50 Table conc 42. 12 l5. 26 Table tail flot 6. 45 47. 19

Minus mesh size (fine fraction) Condition pulp with 0.64 lb./ton NazSiOa.

Float at 25.7 solids.

Reagents-lbs./ton-alcohol frher-0.126 to rougher, 0.54 to cleaner.

Rougher. time- 4 minutes. Cleaner time-3 Referring now specically to the flow scheme of Figure 2, a second flow scheme is described in which the same crude Brazilian run of mine coal is crushed and the crushed coal subjected to a screening operation t0 produce an undersized -35 mesh and an oversize plus 35 mesh which is returned to the crushing. circuit. The undersize or -35 mesh feed is subjected to a froth flotation treatment without further sizing to produce a concentrate and tail. The flotation concentrate is then subjected to a. tabling operation to produce a clean coal concentrate and a tailing containing a relatively high percentage of pyrite. The flotation tailing is likewise subjected to a separate tabling operation to produce a concentrate of pyrite suitable foracld manufacture and a tailing waste. The data in the following example illustrates the recovery of clean coal and pyrite product when the now scheme of Figure 2 y is followed.

Example 2 Results Product Weight Ash I S Flot. R. tail Table oonc. (cl. conc.). Table tail (from cl. conc.). Table conc. (R. tail retreat) Table tail (R. tail retreat) What I claim is: l A method of recovering. pyrite and coal values from a low grade coal containing pyrite which comprises the steps of crushing the coal to -35 mesh, separating the crushed coal into a -35+65 mesh fraction and a -65 mesh fraction, subjecting each fraction to a separate froth flotation operation and tabling separately the otation concentrates to recover the coal values and tabling separately the fioatation tailings to recover the pyrite values, said otation operations being carried out employing a reagent combination comprising a hydrocarbon oil and a frothing agent.

STEPHEN E. ERICKSON.

t CERTIFICATE 0F CORRECTION. v Patent'-No.j2.,55o,lf(9.A september 28, 1915.

ERICKSON..

It is hereby c:certified thatl eror" appears in the printe specification of the `above* xiumbere'dpgt'ent requirflfxgo'I-'rection ex-follows: Page 2, fir-st be read with cple oore'c'ton therein thatjzhe seme signed and sealed'tms 16th dq f Noember, A. D.' 1915.

A I Henry Van Ars'dgle, (Seal) I` l Acting Coxgxgesione'r of Patents. 

